Tellurium alloy rectifier



UNITED sTATEs-PATENT oFFic TELLURIUM ALLOY'RECTIFIER Edgar A. Harty,Marblehead, Mass., assig nor to" General Electric Company, a.corporation of New York Application May 10, 1932, Serial No. 610,386

Claims. (Cl. 175-366) My invention relates to alternating current of thecrucible or lined autoclave, then a layer rectifiers of the type whichcomprises a plurality of broken tellurium metal 18 is placed on the ofconductive members spaced apart by a thin film SOdium, the CODper 19 iSadded, and the remainor spacer of insulating material, and particularlyiflg tellurium 20 iS placed On tOp Of the OODIJeI'.

5 to such rectifiers comprising a plurality of ele- The autoclave isthen sealed and by means of ments composed of tellurium alloy in contactsuitable Diping 21 the air iS evacuated and nitrowith a plurality ofelements composed of another gen under a pressure Of 5 tO 101bS.De1'Square ineh metal, sueh as magnesium, which has a i-eadily isintroduced. The autoclave is then heated and formed and stable oxide,maintained at a temperature of 600 'C. for a time io Reetifiersemp1oying teiiui'ium alloy e1ements sufiicient to insure that itsinterior reaches that have been disclosed in Letters Patent to Hollnageltemperature. and Winckler, No. 1,866,351, filed January 29, ThepllI'pOSe Of Dlaeing the material in the 1927, and issued July 5, 1932.If, is the object of autolave 'is to prevent Sputtering of the alloy mypresent invention to provide an improved, which takes place as soonasthe sodium and 15 method of oonstriioting the active eiements oftellurium melt, the combning of these elements rectifiers of thetellurium type such as disclosed being aeOOmpahied in the alltOelaVe bya SOme'. in the above-mentioned patent of Hollnagel and What VlOiehteXDiOSiOn. The nitrOgen iS em- Winok1erployed to prevent losing anysodium, which might i My invention will be better understood from theCOmhiHe With Oxygen present in air; the nitrOgen 20 followingdescription when considered in confurther acts as a cushion to reducethe violence of neetion With the aoeompanying drawing and its theexplosion. As soon as the interior of the i scope W111 be pointed out inthe appended eiaims autoclave has reached 600 C., all of the elementsReferring to the drawing, Fig. 1 illustrates a placed therein' are in amolten condition and no rectifier enclosed within a container andembodymOre Splittering Oeeurs. The heat 'is then turned 25 ing telluriumalloy elements constructed in ac- Off, the IIitI'Ogen is exhausted, andthe autoclave cordance with my invention; Fig. 2 illustrates is Opened-1h Order tO Open the autoclave it is apparatus utiiized in earryihg outa 'process of necessary to allow air to flow into the vessel. formingtellurium alloy elements in accordance otherwise it W111 he dimelllt 01'imDOSSihle tO Open With my invention; and Fig. 3 i"lustrates a rectifierthe vessel heCaliSe Of the Vae'uum which will be 30 similar to thatshown in Fig. 1 but having a casing preseflt- The plpmg Systemluustrated in .F13- 2 foi'med of a synthetio resin moteriet permits theready introduction of air into the In Fig 1 is shown a i-eetifieium't 10adapted to vessel for the above purpose. After the autoclave beconnected to suitable circuits (not shown) and S Opehed a quartzStiri'ihg I'Od iS used to Stir up eomprising a piuraiity of e1ements 11made of the melt to ensure that a thoroughly mixed alloy 35 telluriumalloy each in contact With a magnesium Will be obtained' NO heat Sapplied 'C0 the mix' sheet 12, the magnesium sheets being in contacttlll'e after the ailtOCiaVe iS Opehed- When the With copper sheets orhiaoes 13, The reetifier zetemperature of the melt reaches 450 C. it issembly 10 is mounted within a, casing 14 in amanpoured into a suitablepreheated die which perner 'and for a purpose to be explained more fullymitS the Casting Of fiat plates Of tellurium alloy, 40 hei-einofterl forexample plates li" x 1" x 1.

In formng the tellurium alloy elements 11 it After preparing the castalloy plates it is neceshas been proposed to use a combination oftelsary to grind the plates in order to make them lurium, copper, and asmall quantity o`f sodium. sufiiciently flat. The grinding operation isper- When the sodium was introduced into the alloy, for-med preferablyby means of asuction holder in 45 however, a more or less violentreaction took place which several of the alloy plates are ground at 10aeeOmpaIiied by SDiltterihg Of the eliOy- I have a time against arotating flat plate on which #1 developed a method of treatment of thetellurium or #2 sandpaper is giued. alloy materials whereby the violenceof the re- The magnesium plates 12 of rectangular Shape, action iSminimizedfor example l x 11/2 and .015" thick, are 50 FOX' theDi'epe'l'a'tiOn Of the ailOy, in B'COOI'dehOe punched out by means of .asuitable die and are With my inVentiOn I empley the pparatus ShOWnpressed in order to present a flat surface. Grease in Fig. 2 wherein 15represents a metal autoclave is removed from the surface of themagnesium lined with refractory material 16, or an autoclave plate bywashing the plates in alcohol and drying having placed therein anenamelled' crucible with with tissue paper, and glaze and oxide are re-55 cover. The sodium 17 is placed in the bottom moved by rubbng theplates on #0 sandpaper.

The electrochemical formation of rectifier elements or cells eachcomprising a tellurium alloy plate 11 and a magnesium plate 12 consistsin first wetting the surface of the magnesium with distilled water toobtain a uniform film. The tellurium alloy plate, which was previouslyground flat as above described, is then placed on the wetted magnesiumsurface, care being taken that no relative motion takes place betweenthe plates. This combination element or cell constituted by a singletellurium alloy plate 11 in contact with a single magnesium plate 12 is`placed in a holder under a pressure of the order of 5 pounds and analternating. current of about'i amps. at from 5 to 8 volts is caused topass through it. This process causes a film to appear between thetellurium alloy and' the magnesium, the film having very markedrectifying properties. At the start of the operation the alloy and themagnesium react and a black film appears. However, the heat of thecurrent dries up the water and a welding action then takes place. Thiswelding action starts at the center of the plates and travels around theunited surfaces of the plates-until after about an hour the weldingeffect is visible around the edges. This action has a tendency to weldthe tellurium alloy and magnevsium together so that a single rectifyingunit is obtained, or single rectifier cell, which may be utilized in anydesired rectifier combination. For example rectifier units so formedmaybe used under the severe conditions of battery charging in which thevoltage impressed upon the rectifier when its anode is negative, beingequal to the sum of the line voltage and the battery voltage.

Tellurium alloy elements for'rectifier use have comprised heretofore alarge proportion of tellurium, for example 93 parts, and a relativelysmall proportion of copper, for example '7 parts, the copper being addedto, compensate for the high resistance of the tellurium when used alone.I have found, however, that the rectifying action of the tellurium alloyelements is markedly improved by forming the alloy of tellurium, copperand silver. Thus a rectifier comprising, in accordance with myinvention, alloy elements having substantially 97% parts tellurium, 2parts copper and 21/2 parts silver shows in operation a considerabledecrease in cell drop and leakage current over the rectifiershereinbefore described having tellurium and copper alloy elements. Insome instances I have found it desirable to form the alloy ofsubstantially 971/2 parts tellurium, 2 parts copper, 21/2 parts silver,and l/z part sodium. v

In developing the tellurium alloy rectifier it was observed thatrectifier elements not on load and unheated had a tendency to absorbmoisture from the atmosphere and that the film present between thetellurium alloy and the magnesium elements became powdered. It was foundthat moisture creeping between the rectifier plates caused the powderingtrouble. To avoid this difiiculty it has been suggested to seal up theedges of the rectifier elements by means of varnishes, for example in acontainer 14 and seal the cells formed by the rectifier elements 11, 12by fillng the container with a suitable compound 22. The rectifier isconnected across a battery -in such a way as to cause the leakagecurrent to flow thereby heating the rectifier elements, and the hotcompound is poured into the container while the cur: rent is flowingthrough the rectifier.

A sealing compound to be satisfactory for the purpose of protecting thetellurium alloy and magnesium rectifier cell from the effects ofmoisturemust have the following propertiesz-it must be stable and not decomposechemically at the Operating temperature of the rectifier, 50 to 60 C.:it must be hard or pasty at this Operating temperature; it must notcontain free acid, such as hydrochloric acid, having a tendency toattack the magnesium element.

The effectiveness of this method of sealing the rectifier elementsagainst powdering vof the film between the tellurium alloy and themagnesium by moisture is such that after 2000 hours exposure to moistatmosphere. no change occurs in the direct current characteristics ofthe rectifier. Rectifiers in their unsealed state can not be operatedintermittently since as above explained they absorb moisture during theidle periods and cease to rectify. Unsealed units when run continuouslyare hot and, therefore, under usual favorable atmospheric conditionscannot absorb suflicient moisture to damage them, but under unusualconditions, such as Operating the unsealed units in a damp cellar, theseunsealed units absorb moisture even while heated by the current, andstop rectifying. However, rectifier units sealed, in accordance with myinvention, in a casing filled with compound as shown in Fig. 1, andoperated under the above extreme conditions of dampness show no changeswhatever.

In Fig. 3, instead of mounting the rectifier units 10 comprising thetellurium alloy plates 11, magnesium plates 12 and copper sheets 13 in ametal or other container filled with sealing compound as shown in Fig.2, the rectifier unit is molded, in accordance with my invention, in aSynthetic resin compound 22 preferably of the type comprisingphenol-aldehyde condensation products. The Synthetic resin compoundseals the rectifier) elements from the deteriorating effects ofmoisture, and on hardening forms in itself a casing for the rectifierunit or units. Thus is produced a compact unitary rectifier structurewhich may include connection means such as prongs (no'r shown) moldedinto the resin and similar to those of a vacuum tube. the rectifierstructure then being capable of being plugged into a suitable outlet orsocket as on the transformer of a loudspeaker or the like.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In a rectifier, a tellurium alloy element comprising a relativelylarge proportion of tellurium, a relatively small proportion of copper,and a relatively small proportion of silver.

' 2. In a rectifier, a tellurium alloy element comprising tellurium,copper, silver, and a relatively small portion of sodium.

3. In a rectifier, a tellurium alloy element comprising substantially971/2 parts of tellurium, 2 parts of copper, and 21/ parts of silver.

4. In a rectifier, a tellurium alloy element comprising substantially971/2 parts of tellurium, 2

, parts of copper, 21/2 parts of silver and 1/2 part of sodium.

5. The process of manufacturing a tellurium alloy element for analternating current rectiiier, said alloy including copper and arelatively small portion of sodium, which compr'ises melting theconstituents of said alloy in an atmosphere of nitrogen. z

6. The process of manufacturing a tellurium alloy element for analtemating current rectiiier, said alloy including a relatively smallportion of sodium, which comprises heating the constltuents of saidalloy in an atmosphere of nitrogen to a temperature'of the order of 600C.

7. The process of manufacturing an alternat- 'in'g current rectifierelement including tellurium;

copper and sodium which comprlses heating said metals in an atmosphereof nitrogen to a temperature of the order of'600` C.

10. The process of manufacturing an alternating current rectifierelement including tellurium and sodium which comprises placing saidsodium in the bottom of an autoclave, placing said tellurium above saidsodium, evacuating the air from said autoclave, introducing nitrogeninto the interior of said autoclave. and heating said i autoclave longenough to produce a temperature in the interior. thereof of the order of600? C.-

11. The process of manufacturing an alternating current `rectinerelement including tellurium, copper and sodium which comprises placingsaid sodium in the bottom of an autoclave, placing a portion of saidtellurium on said so'dium, placing said copper on saidvpomon of thetellurium, placing the rest of the tellurium on said copper, evacuatingthe air from said autoclave.

introducing nitrogen at a pressure of the order .of 5 to 10 pounds persquare inch into the interior of said autoclave, and heating saidautoclave long 'enough to produce a temperature in the interior thereofof the order of 600 C.

12. A rectifler unit comprising a plurality of elements of thetellurium-copper alloy type, said alloyincluding a portion of silver,each of said elements being in contact with an element composed of.another metal forming afifllm between said alloy and said other metal,means to protect said film from the eifects of absorbed moistureincluding acasing containing, said element and a compound within saidcasing to seal the ,contacting edges of said element.

13. A lrectii'ier'- unit compr'ising a plurality of elements of. thetellurium-copper alloy type, said alloy including a portion of silver,each of said elements being in contact with an element composedofanother metal forming a fllm lbetween said alloy and said other metal,means to protect said nlm from the eifects of absorbed moistureincluding a mass of synthetic resin of the type comprisingphenol-aldehyde condensation products in which said elements are molded.

14. The method of protecting the film between tellurium alloy elementsand magnesium elements of a rectifier from the effects of moisture whichcomprises passing a heating electric current between said elements, andembedding said elements in a sealing compound while said current isilowint.` 4.

15; The method of preventing the powdering of the film betweentellurium-alloy elements and magnesium elements of a rctifler due to theeffects of moisture, which comprises causing leakage current to flowbetween said elements to heat

